If anyone could be considered a Russian counterpart to the infamous British double-agent Kim Philby, it was Oleg Gordievsky. The son of two KGB agents and the product of the best Soviet institutions, the savvy, sophisticated Gordievsky grew to see his nation's communism as both criminal and philistine. He took his first posting for Russian intelligence in 1968 and eventually became the Soviet Union's top man in London, but from 1973 on he was secretly working for MI6.

Eddie Chapman was a charming criminal, a con man, and a philanderer. He was also one of the most remarkable double agents Britain has ever produced. Inside the traitor was a man of loyalty; inside the villain was a hero. The problem for Chapman, his spymasters, and his lovers was to know where one persona ended and the other began.

Who was Kim Philby? Those closest to him—like his fellow MI6 officer and best friend since childhood, Nicholas Elliot, and the CIA’s head of counterintelligence, James Jesus Angleton—knew him as a loyal confidant and an unshakeable patriot. Philby was a brilliant and charming man who rose to head Britain’s counterintelligence against the Soviet Union. Together with Elliott and Angleton he stood on the front lines of the Cold War, holding Communism at bay. But he was secretly betraying them both: He was working for the Russians the entire time.

As the American hostage crisis in Iran boiled into its seventh month in the spring of 1980, six heavily armed gunman barged into the Iranian embassy in London, taking twenty-six hostages. What followed over the next six days was an increasingly tense standoff, one that threatened at any moment to spill into a bloodbath.

In 1942, in a quiet village in the leafy English Cotswolds, a thin, elegant woman lived in a small cottage with her three children and her husband, who worked as a machinist nearby. Ursula Burton was friendly but reserved, and spoke English with a slight foreign accent. By all accounts, she seemed to be living a simple, unassuming life. Her neighbors in the village knew little about her. They didn’t know that she was a high-ranking Soviet intelligence officer. They didn’t know that her husband was also a spy, or that she was running powerful agents across Europe.